Frequency Division Multiple Access (FDMA) is a multiple access technique that assigns individual frequency bands or channels to each user. FDMA avoids interference by ensuring each user is allocated a unique frequency band. While FDMA allows multiple users to access the channel simultaneously and has low inter-symbol interference, it requires tight RF filtering to minimize adjacent channel interference and duplexers, increasing costs. Non-linear effects from power amplifiers can also cause intermodulation frequencies, interfering with adjacent channels. The capacity of an FDMA system is calculated based on the total spectrum allocation, guard band allocation, and channel bandwidth.

1. FREQUENCY
DIVISION
MULTIPLE
ACCESS

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3. Multiplexing Vs Multiple Access
Multiplexing (or muxing) is a way of sending multiple
signals or streams of information over a communications
link at the same time in the form of a single, complex
signal;
Multiple Access is a technique used to allow multiple
users to access the channel at the same time without any
interference. In other words,
Multiple Access is a application of Multiplexing

4. Frequency Division Multiple Access - FDMA
USER 1
USER 3
USER 2
GUARD BANDS
To avoid interference

5. FDMA
• FDMA Assigns individual channels to individual users
• Each user is allocated a unique frequency band or channel
• The channels are assigned on demand by the users
• The same frequency is not allotted for 2 different users.
• The bandwidth of FDMA channel is relatively narrow (30Khz)
• FDMA are usually implemented in narrow band systems
• The amount of inter symbol interference is low and thus No euqalization is required in FDMA
narrow band systems
• FDMA is continuous transmission systems where as it required less Overhead compared to TDMA
• FDMA uses Duplexers since both the transmitter and receiver operates at the same time. This
results in increase in COST of FDMA
• FDMA requires tight RF filtering to minimize adjacent channel interference

6. Non Linear Effects in FDMA
• In FDMA, Many channels share the same
antenna at the base station.
• In order to get the Maximum Power
Efficiency the Power Amplifiers and
Power Combiners are operated at (or)
near Saturation Region
• At (or) near Saturation Region the Power
amplifiers and power combiners are Non
Linear.
• These non linearities causes signal
spreading in the frequency domain and
generate Intermodulation (IM)
Frequencies.
• These Spreading will interfere with
adjacent channels causing adjacent
channel interference.

7. Capacity of FDMA
• The number of channels that can be simultaneously supported in
FDMA systems is given by
N=(Bt – 2 Bguard) / Bc
• Where
• Bt is the total spectrum allocation
• Bguard is the guard band allocation at the edge of allocated spectrum
• Bc is the channel bandwidth

8. Summary
• Multiplexing Vs Multiple Access
• Multiple Access is an application of Multiplexing
• Type of Multiple access Techniques
• Frequency Division Multiple Access Technique
• Principle of Operation
• Pros and Cons
• Non Linear Effects of FDMA
• Channel Capacity of FDMA systems